Lens system having a large aperture and long focal length

ABSTRACT

A lens system having a large aperture and a long focal length, which is constructed as five components and five lenses and consists of first, second and third components of positive meniscus lenses, each having at its object side a convex surface, a fourth component of a negative meniscus lens that has at its object side a convex surface, and a fifth component of a positive lens separated from the fourth component by a large air space, all lenses being arranged in succession from the side of an object, and which is defined by the following five conditions, i.e.

T v T United States 111 3,749,478 Nakagawa et al. July 31, 1973 1 LENSSYSTEM HAVING A LARGE 57 ABSTRACT APERTURE AND LONG FOCAL LENGTH A lenssystem having a large aperture and a long focal [75] Inventors: JiheiNakagawa; Sumio Nakamura, length, whlch is colfstrucled as fivecompomfms and both f Tokyo Japan five lenses and consists of first,second and th1rd components of positive meniscus lenses, each having atits [73] Asslgnee: Olympus optical company named object side a convexsurface, a fourth component of a Tokyo Japan negative meniscus lens thathas at its object side a con- [22] Filed; AP 7 7 vex surface, and afifth component of a positive lens separated from the fourth componentby a large air [21] ll N04 241,927 space, all lenses being arranged insuccession from the side of an object, and which is defined by thefollowing [30] Foreign Application Priority Data f g rn jg i l 6 "1 z a2 Apr. l0, [971 Japan 46/22087 2' 3f fa 1.1..

3. n 1.7 l. 0 l7 4 5?} 3.5 51. ..i.t..fi20 2i9/63 0mm 58 Field of Search350/216 and 48 where f is a composite focal length of the total lenssys- [56] Rdcrences Cited tem, f is a focal length of the thirdcomponent, f is a composite focal length of the first, second and thirdUNITED STATES PATENTS components, n n,, n, are refractive indices of thegag :35: al. 7? successive lenses counted from thhe object side, T 13,236,151 2/I966 Solisch et al 350/2l6 are Abbe 8 numbers e success've'cnses counted from the object side, and d,, d,, .d, are axialthicknesses of the successive lenses or air spaced be- PrimaExaminer-John K. bin

Ty Cor tween the successive lenses.

AttorneyEric H. Waters et al.

3 Claims, 7 Drawing Figures d3 d4 d6 LENS SYSTEM HAVING A LARGE APERTUREAND LONG FOCAL LENGTH This invention relates to a lens system having alarge aperture and a long focal length.

Heretofore, it has been well known to construct one of the Ernostar typelens systems having a long focal length by a first component of apositive lens, a second component of a composite positive meniscus lens,meniscus third component of mensicus negative meniscus lens, andmeniscus fourth component of positive lens. This type of lens system hasthe disadvantage that if the telephoto ratio (the ratio of the distancebetween the front surface of the first lens component and the filmsurface to the focal length) is made small, the various aberrationsbecome degraded with the result that a large aperture could not beobtained.

The object of the invention is, by breaking up the second component ofcomposite positive meniscus lens of the conventional lens system intotwo lenses and by changing the composite negative lens having a weakrefractive power into a positive meniscus lens having a weak refractivepower, to provide a lens system having an aperture ratio of the order of2.8 and a long focal length whose telephoto ratio is on the order of0.93 and having significantly corrected aberrations, and moreparticularly having significantly corrected coma and astigmatism withrespect to light rays having a large incident angle.

A feature of the invention is the provision of a lens system having alarge aperture and a long focal length, which is constructed as fivecomponents and five lenses and consists of first, second and thirdcomponents of five positive meniscus lenses, each having at its objectside a convex surface, a fourth component ofa negative meniscus lensthat has at its object side a convex surface, and a fifth component of apositive lens separated from the fourth lens component by a large airspace, all lenses being arranged in succession from the side of anobject, and which is defined by the following five conditions, i.e.

5. u, 50, 11 50 and r1; 48 where f is a composite focal length of thetotal lens system, f, is a focal length of the third lens component, fis a composite focal length of the first, second and third lenscomponents, n n n, are refractive indices of the successive lensescounted from the object side, 11,, u, 11,, are Abbe's numbers of thesuccessive lenses counted from the object side, and d d d, are axialthicknesses of the successive lenses or air spaces between thesuccessive lenses.

For a better understanding of the invention, the same will be explainedby reference to the accompanying drawings, in which:

FIG. 1 shows in cross-section a lens system having a large aperture anda long focal length constructed according to the invention;

FIGS. 2a to show aberration characteristic curves of one exemplaryembodiment of the invention; and

FIGS. 3a to show aberration characteristic curves of another exemplaryembodiment of the invention.

Referring to the drawings, a lens system having a large aperture and along focal length according to the invention is shown in FIG. 1 in whichL 1.: and L, designate first, second and third components of positivemeniscus lenses, each having at its object side a convex surface,respectively. L. shows a fourth component of a negative meniscus lensthat has at its object side a convex surface. L illustrates a fifthcomponent a positive lens separated from the fourth component L, by alarge air space d,,. These lenses L L L L, and L, are arranged insuccession from the side of an object (not shown).

In accordance with the invention, the refractive indices, focal lengthsand Abbes numbers of the successive lenses are chosen such that they aredefined by the following five conditions, i.e.

5.11,, 11 5O, :1 48 where f is a composite focal length of the totallens system, f; is a focal length of the third component lens, f is acomposite focal length of the first, second and third components lenses,n,, n u are refractive indices of the successive lenses counted from theobject side, 1 V2, 1 are Abbe's numbers of the successive lenses countedfrom the object side, and (1,, d d, are axial thicknesses of thesuccessive lenses and air spaces between the successive lenses.

In accordance with the invention the use of a lens having a relativelyhigh refractive index as defined by the condition 1 as the threepositive lenses of the first, second and third lens components rendersit possible to provide excellent correction of spherical aberration,coma, etc. If the condition 1 is not satisfied, the radii of curvaturesof the first, second and third lens components become small, therebyproducing spherical aberration, with the result that it is difficult toobtain a lens system having a large aperture. If it is intended tocorrect such spherical aberration by increasing curvatures of theselenses, satisfactory removal of the coma and astigmatism could not beattained.

The condition 2 shows that the focal length f; of the third lenscomponents L is relatively long if compared with the first and secondgroups of lenses L and L,. If f 3f, the share of the third lenscomponent L, to correct the aberrations becomes decreased so that theshare of the first and second lens components L and L to correct theaberrations becomes increased, whereby favorable correction of coma,etc. could not be effected. lffl, 4], it is difficult to make thetelephoto ratio small and to correct the various aberrations.

The condition 3 that the refractive index of the fourth lens component Lshould be larger than 1.7 prevents the Petzval sum from becoming small.Thus, a suitable increase of the radius of curvature of the fourthcomponent of a negative lens L is capable of significantly correctingthe coma. If n, is smaller than 1.7, the Petzval sum becomes surplus incorrection so that the definition resolving power in the sagittaldirection on the periphery of the picture surface becomes degraded.Moreover, if n, 1.7, the radius of curvature r,, is increased to degradethe aberration out of axis.

In the condition 4, if d,+d,+d,+d +d -,+d, is smaller than 0.121, it isnot only difficult to make the telephoto ratio small, but also thevarious aberrations become degraded. If d +d +d +d +d +d is larger than0.24f, the Petzval sum becomes negative which is not desirable.

In the condition 5, v, 50 and 1/ 50 are conventional means of correctingthe chromatic aberration and 11 48 is consistent with the condition 2.The condition 5 is effective to significantly correct both theaberrations on axis and the magnification chromatic aberration. If u 50and 11 50, it is impossible to make r1 48. If v, 48, both theaberrations on axis and the magnification chromatic aberration could notbe significantly corrected.

The invention will now be described with reference to the followingexamples.

The aberration characteristic curves of the present embodiment are shownin FIGS. 20, 2b and 20. FIG. 2a shows the spherical aberrations and thesine condition (S.C.), FIG. 2b shows the astigmatisms and FIG. 2c showsthe distortion.

As seen from these aberration characteristic curves, the lens systemaccording to the present embodiment makes it possible to significantlycorrect various aberrations.

l. A lens system having a large aperture and a long focal length, whichis constructed as five components and five lenses and consists of first,second and third components of positive meniscus lenses, each having atits object side a convex surface, a fourth component of a negativemeniscus lens that has at its object side a convex surface, and a fifthcomponent of a positive meniscus lens separated from the fourthcomponent by a large air space, all lenses being arranged in successionfrom the side of an object, and which is defined by the following fiveconditions, i.e.,

5.11, 50, v, and v 48 where f is a composite focal length of the totallens system, f is a focal length of the third components, f, is acomposite focal length of the first, second and third components, n n nare refractive indices of the successive lenses counted from the objectside, 11,, v

u are Abbes numbers of the successive lenses counted from the objectside, and d,, d d are axial thicknesses of the successive lenses or airspaces between the successive lenses.

2. A lens system having a large aperture and a long focal length, whichis constructed as five components and five lenses and consists of first,second and third components of positive meniscus lenses, each having atits object side a convex surface, a fourth component of a negativemensicus lens that has at its object side a convex surface, and a fifthcomponent of a positive lens separated from the fourth component by alarge air space, all lenses being arranged in succession from the sideof an object, and which is defined by the following five conditions,i.e.,

f fa fl.2.3

5. v, 50, 11 50 and 11 48 where f is a composite focal length of thetotal lens system, f;, is a focal length of the third components, f is acomposite focal length of the first, second and third components, n,,n,, u are refractive indices of the successive lenses counted from theobject side, 11,, v 11,, are Abbes numbers of the successive lensescounted from the object side, and d d d, are axial thicknesses of thesuccessive lenses or air spaces between the successive lenses, whereinFl .0, f, =0.392 andf;;=2. l 76; and wherein r to r d to d n, to n; andv, to 11,, are defined by the following values:

3. A lens system having a large aperture and a long focal length, whichis constructed as five components and five lenses and consists of first,second and third components of positive meniscus lenses, each having atits object side a convex surface, a fourth component of a negativemeniscus lens that has at its object side a convex surface, and a fifthcomponent of a positive lens separated from the fourth component by alarge air space, all lenses being arranged in succession from the sideof an object, and which is defined by the following five conditions,i.e.

5.11, 50, :1 50 and v 48 where f is a composite focal length of thetotal lens system, f, is a focal length of the third components, f is acomposite focal length of the first, second and third components, n,, n,n, are refractive indices of the successive lenses counted from theobject side, v,, 11,,

. 11 are Abbes numbers of the successive lenses counted from the objectside, and d,, 11,, d, are axial thicknesses of the successive lenses orair spaces between the successive lenses; wherein f=l .0, f, =0.407 andf,=2.0; and wherein r to r d, to (1,, n to n and v, to v, are defined bythe following values:

1. A lens system having a large aperture and a long focal length, whichis constructed as five components and five lenses and consists of first,second and third components of positive meniscus lenses, each having atits object side a convex surface, a fourth component of a negativemeniscus lens that has at its object side a convex surface, and a fifthcomponent of a positive meniscus lens separated from the fourthcomponent by a large air space, all lenses being arranged in successionfrom the side of an object, and which is defined by the following fiveconditions, i.e.,
 1. n1+n2+n3/3 > 1.6,
 2. 3f > f3 > 4f1,2,3,
 3. n4 >1.7,
 4. 0.24f > d1+d2+d3+d4+d5+d6 > 0.12f, and
 5. Nu 1 > 50, Nu 2 > 50and Nu 3 < 48 where f is a composite focal length of the total lenssystem, f3 is a focal length of the third components, f1,2,3 is acomposite focal length of the first, second and third components, n1, n2. . . n5 are refractive indices of the successive lenses counted fromthe object side, Nu 1, Nu 2, . . . Nu 5 are Abbe''s numbers of thesuccessive lenses counted from the object side, and d1, d2, . . . d9 areaxial thicknesses of the successive lenses or air spaces between thesuccessive lenses.
 2. 3f > f3 > 4f1,2,3,
 2. 3f > f3 > 4f1,2,3
 2. 3f >f3 > 4f1,2,3,
 2. A lens system having a large aperture and a long focallength, which is constructed as five components and five lenses andconsists of first, second and third components of positive meniscuslenses, each having at its object side a convex surface, a fourthcomponent of a negative mensicus lens that has at its object side aconvex surface, and a fifth component of a positive lens separated fromthe fourth component by a large air space, all lenses being arranged insuccession from the side of an object, and which is defined by thefollowing five conditions, i.e.,
 3. n4 > 1.7,
 3. A lens system having alarge aperture and a long focal length, which is constructed as fivecomponents and five lenses and consists of first, second and thirdcomponents of positive meniscus lenses, each having at its object side aconvex surface, a fourth component of a negative meniscus lens that hasat its object side a convex surface, and a fifth component of a positivelens separated from the fourth component by a large air space, alllenses being arranged in succession from the side of an object, andwhich is defined by the following five conditions, i.e.
 3. n4 > 1.7, 3.n4 > 1.7,
 4. 0.24f > d1+d2+d3+d4+d5+d6 > 0.12f, and
 4. 0.24f >d1+d2+d3+d4+d5+d6 > 0.12f, and
 4. 0.24f > d1+d2+d3+d4+d5+d6 > 0.12f, and5. Nu 1 > 50, Nu 2 > 50 and Nu 3 < 48 where f is a composite focallength of the total lens system, f3 is a focal length of the thirdcomponents, f1,2,3 is a composite focal length of the first, second andthird components, n1, n2 . . . n5 are refractive indices of thesuccessive lenses counted from the object side, Nu 1, Nu 2, . . . Nu 5are Abbe''s numbers of the successive lenses counted from the objectside, and d1, d2, . . . d9 are axial thicknesses of the successivelenses or air spaces between the successive lenses.
 5. Nu 1 > 50, Nu 2 >50 and Nu 3 < 48 where f is a composite focal length of the total lenssystem, f3 is a focal length of the third components, f1,2,3 is acomposite focal length of the first, second and third components, n1,n2, . . . n5 are refractive indices of the successive lenses countedfrom the object side, Nu 1, Nu 2, . . . Nu 5 are Abbe''s numbers of thesuccessive lenses counted from the object side, and d1, d2, . . . d9 areaxial thicknesses of the successive lenses or air spaces between thesuccessive lenses, wherein f 1.0, f1,2,3 0.392 and f3 2.176; and whereinr1 to r10, d1 to d9, n1 to n5 and Nu 1 to Nu 5 are defined by thefollowing values: r1 0.3847 d1 0.0392 n1 1.63854 Nu 1 55.38 r2 1.5003 d20.0007 r3 0.3465 d3 0.0317 n2 1.617 Nu 2 62.79 r4 0.5969 d4 0.0025 r50.3748 d5 0.0638 n3 1.70154 Nu 3 41.1 r6 0.4620 d6 0.0260 r7 0.9685 d70.0409 n4 1.7847 Nu 4 26.22 r8 0.1957 d8 0.2758 r9 0.6435 d9 0.015 n51.80518 Nu 5 25.43 r10 1.8672
 5. Nu 1 > 50, Nu 2 > 50 and Nu 3 < 48where f is a composite focal length of the total lens system, f3 is afocal length of the third components, f1,2,3 is a composite focal lengthof the first, second and third components, n1, n2 . . . n5 arerefractive indices of the successive lenses counted from the objectside, Nu 1, Nu 2, . . . Nu 5 are Abbe''s numbers of the successivelenses counted from the object side, and d1, d2, . . . d9 are axialthicknesses of the successive lenses or air spaces between thesuccessive lenses; wherein f 1.0, f1,2,3 0.407 and f3 2.0; and whereinr1 to r10, d1 to d9, n1 to n5 and Nu 1 to Nu 5 are defined by thefollowing values: r1 0.4011 d1 0.0472 n1 1.58913 Nu 1 61.11 r2 2.3231 d20.0042 r3 0.3213 d3 0.0336 n2 1.56873 Nu 2 63.16 r4 0.5016 d4 0.0025 r50.3406 d5 0.0639 n3 1.70154 Nu 3 41.1 r6 0.4159 d6 0.0261 r7 0.8450 d70.0389 n4 1.7847 Nu 4 26.22 r8 0.1960 d8 0.2578 r9 0.6486 d9 0.0255 n51.7847 Nu 5 26.22 r10 1.7995.